In recent years, the proliferation of wireless devices has created a need for support devices, such as wireless repeaters and access points, to maintain service coverage in indoor locations. Virtually every cellular telephone user has experienced a loss or degradation of service in certain indoor locations, particularly in home and business locations. The reduction in communication coverage or signal strength also causes the cellular telephone to increase its transmit power, which quickly drains the battery. To correct this problem, wireless repeaters can be deployed to improve indoor communication reception. These devices are typically mounted in a convenient place and connected by a coaxial cable to an antenna to improve communication signal strength in a desired location. Antennas are in constant demand for wireless repeaters, and those that are low cost, easy to install and aesthetically pleasing have considerable advantages. The same type of antenna, besides being used with a wireless repeater, may also be used as for as a wireless access point, a wireless Internet node, as part of a local area network (LAN) and with various kinds of other indoor communication devices.
Wireless telephone systems operate at a number of carrier frequencies, such as the analog cellular carrier frequency band between 824 MHz and 894 MHz, and the PCS and GSM digital system carrier frequency bands of 1850 MHz through 1990 MHz in the United States and 1710 MHz through 2170 MHz in Europe and Japan. Wireless Internet nodes and wireless LAN access points can operate at higher carrier frequencies, such as the WiFi band near 2400 MHz. As a result, it is advantageous for one access point antenna to operate acceptably throughout a relatively wide frequency bandwidth so that the same antenna can be used for all available wireless communication applications, now generally in the range from approximately 800 MHz through 2400 MHz. Unfortunately, conventional wireless access points do not have this bandwidth capability. These antennas should also provide good omni-directional reception, which for a ceiling mounted antenna amounts to approximately 360° azimuth and 180° elevation coverage below the ceiling.
For example, U.S. Pat. No. 6,369,766 to Strickland et al. (assigned to the assignee of the present application) describes an omni-directional antenna having an asymmetrical bi-cone as a passive feed for a antenna element. This relatively low profile antenna achieves good performance and excellent coverage. Like other known conventional antennas designed for indoor use, however, this antenna only operates at a narrow frequency bandwidth about the 2400 MHz standard for wireless Internet nodes and LAN access points, and therefore cannot also accommodate wireless telephone service.
One recent attempt to provide an indoor antenna with wider bandwidth is the monopole antenna offered by Huber and Suhner, Inc. This antenna is designed for suspension beneath a ceiling and the radiating element has a non-planar shape. The profile of the radiating element when viewed from the front has a geometric shape similar to a tree or tree leaf and, when viewed from the side, has a serpentine shape, such that the overall shape of the antenna element is decidedly three-dimensional. The eccentric three-dimensional shape of this antenna is relatively expensive to construct and tends to draw distracting attention to the antenna.
Many indoor antennas have other eccentric shapes that are similarly expensive to construct, ungainly and obtrusive. Often, such antennas also have a somewhat delicate antenna element that needs to be protected from damage by inadvertent contact. To conceal and protect these antennas, they are typically placed within an electrically-transparent, but often visually opaque, radome. The radome adds to the bulk, complexity and cost of the antenna. As a result, a continuing need exists for a wide-band, low cost, easy to install and aesthetically pleasing indoor antenna that does not require a radome.